Air purifying filters are designed to filter out harmful gases (gas filter) or a combination of harmful gases and particulates (combination filter). Gas and vapor purification is provided by sorbent which both physically adsorbs and chemi-sorbs the contaminants preferentially from the air. The filter housing or canister must be designed such that contaminated air may not bypass the sorbent. Typically this is effected by the design and assembly of a sorbent bed. Typical sorbent beds are of uniform thickness with entrance and exit consisting of a flat uniform plane. The uniform plane is typically orientated such that it is normal to the direction of airflow. Sorbent beds that are uniform planes are typically less expensive and easier to manufacture in automated assembly than beds with a curved or conformal shape. Filters containing uniform flat beds do not conform to the wearer's face and body. The non-conformal shape detracts from the wearer's field of view, facepiece fit, and comfort, and leads to designs which are deemed less aesthetically pleasing. Aesthetic designs are important to wearers who must interact with the public without instilling fear (e.g. first responders and healthcare workers). Aesthetically pleasing designs also lead to better worker compliance. Filling of sorbent beds using traditional techniques such as snowstorm filling for conformal non-planar beds usually leads to reduced service life, or immediate breakthrough of contaminants.
It would be desirable to provide a filter that more closely conforms to a user, thus providing a less obtrusive and more comfortable device. Techniques for the assembly of conformal sorbent beds exist. These assembly techniques, however, are non-optimal, are prone to damaging the sorbent during filling, and are limited to near symmetrical conformal shapes with a limited degree of curvature. Materials solutions exist which depend on the use of flexible sorbent media. Such media, however, typically underperforms granular media. Conformal filters of these types either introduce higher inhalation resistance or cannot offer high levels of protection and service life.